Male seahorse gives birth

April 17, 2025 • 2:02 pm

Seahorses (Hippocampus spp.) which are fish, have an unusual reproductive system. The males get “pregnant”, meaning that they carry the eggs, which are deposited in the male’s pouch by the female and then fertilized there. (Note: this doesn’t mean that seahorse males are “females”, or that there are more than two sexes!)  We don’t really know why males gestate the eggs, but we do know that females produce eggs faster than males can gestate them. This means that, unlike most animals, females compete for the attention of males.  Here’s a birth; National Geographic says that 2,000 babies are being born. Wikipedia says that the babies can be as few as 5 or as many as 25.

That’s your biology of the day; and I am sorry that for the next few days I won’t be posting much.

 

17 thoughts on “Male seahorse gives birth”

  2. Thank you Jerry. This clears up a lot for me. I kept reading all the back and forth over the years and could not tease out the simple truth which you have made crystal clear here….and in the end it is quite simple.

  3. There is that brain structure called “hippocampus”. Is there an independent reason, or is that based on some shape resemblance to seahorses?

  4. A quick perusal online, and I learn:
    Fishes commonly guard their eggs in a nest, and there are species where it is the males that do the nest guarding. I think this is common, really.
    There are several species where fishes do mouth brooding of the eggs and fry, and among them are many species where its the males that do it.
    These are still a far cry from males having a special pouch to brood eggs, but it’s a start.

    1. Male Betta fish (Betta splendens) build bubble nests on the water surface for the fertilized eggs. And keep replacing the eggs if they fall out.

  5. This unusual fact actually proves Trivers’ parental investment theory. From “The Ape that Understood the Universe” by Steve Stewart-Williams:

    “Another example of a sex-role-reversed species is the Gulf pipefish: a small fish that looks like a seahorse straightened out with hair straighteners, and that is in fact a close cousin of the seahorse. Like jacanas, Gulf pipefish buck the males-compete/females-choose trend. Female pipefish are ornamented with silver stripes, whereas male pipefish are ultra-choosy about their mates, preferring older, larger females.
    At first glance, the sex-role-reversed species appear to falsify Trivers’ theory. On closer inspection, however, they provide some of the strongest support there is that Trivers hit the nail on the head. That’s because, in all these gender-bending species, the males invest more into offspring than the females. […] Among Gulf pipefish, the males incubate the eggs in a specialized brood pouch. As a result, the females in these species can potentially produce more offspring. Like an anti-gravity machine, this flips all the normal selective forces in the opposite direction, producing male-like females and female-like males – just as parental investment theory would predict.”

    1. The role reversal is pretty rare. But there are birds called the Phalaropes which also do it. As I understand it, males make a big communal ground nest, and various females vie to be allowed to lay eggs in the nest and the males to the rearing. As expected, the ornamentation is reversed.

    2. Wow, John, you are a man of even more talents than I’d realized! This looks great — I’ll check it out.

  7. Don’t let the gender activists hear about this one. “See? We were right. Males can get pregnant.”

  8. “National Geographic says that 2,000 babies are being born. Wikipedia says that the babies can be as few as 5 or as many as 25.”

    Something wrong with those numbers.

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